Applications of Polarizable Continuum Models To Determine Accurate Solution-Phase Thermochemical Values Across a Broad Range of Cation Charge - The Case of U(III-VI)

作者：Parmar Payal^*; Samuels Alex; Clark Aurora E

来源：Journal of Chemical Theory and Computation, 2015, 11(1): 55-63.

DOI：10.1021/ct500530q

Contributing factors to the solution-phase correction to the free energy of the molecular clusters U(H2O)(n)(3+/4+) and UO2(H2O)(m)(1+/2+) (n = 8, 9, 30, 41, 77; m = 4, 5, 30, 41, 77) have been examined as a function of cavity type in the integrated-equation-formalism-protocol (IEF) and SMD polarizable continuum models (PCMs). It is observed that the free energy correction, G(corr), does not smoothly converge to zero as the number of explicitly solvating water molecules approaches the bulk limit, and the convergence behavior varies significantly with cavity and model. The rates of convergence of the gas-phase hydration energy, Delta G(hyd), wherein the bare metal ion is inserted into a molecular water cluster and Delta G(corr) for the reaction exhibit wide variations as a function of ion charge, cavity, and model. This is the likely source of previously reported discrepancies in predicted free energies of solvation for metal ions when using different PCM cavities and/or models. The cancellation of errors in Delta G(hyd) and Delta G(corr) is optimal for clusters consisting of only a second solvation shell of explicit water molecules (n = m = 30). The UFF cavity within IEF, in particular, exhibits the most consistent cancellation of errors when using a molecular cluster consisting of a second shell of solvating water for all oxidation states of uranium, leading to accurate free energies of solvation Delta G(solv) for these species.

• 出版日期2015-1